Digitizer having flat tablet with magnetic shield plate

Abstract

A digitizer for determining coordinate value of a point designated on a given two-dimensional coordinate plane. A pointing instrument is manually operable to designate a point on the given two-dimensional coordinate plane of a tablet. The tablet includes a flat sensor defining the given two-dimensional coordinate plane and operative for transmitting magnetic signal between the flat sensor and the pointing instrument disposed thereon to detect the designated point to thereby produce a detection signal, and a shielding plate disposed under the flat sensor to magnetically shield the flat sensor. The shielding plate is composed of silicon steel containing 4.0 to 7.0 weight % of silicon. A processing circuit is connected to the flat sensor for processing the detection signal to determine the coordinate value of the designated point.

1. A tablet for coupling AC energy to a tuned circuit on an implement adapted to be moved over an external flat surface of the tablet and responsive to AC energy coupled back to the tablet from the tuned circuit, comprising: a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils arranged in two coordinate directions, the loop coils being disposed between the faces for emitting the AC energy coupled to the tuned circuit and responsive to the AC energy coupled from the tuned circuit for generating a signal indicative of the implement position relative to the two coordinate directions; and a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on the loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of the AC energy coupled between the loop coils and tuned circuit. 
     
     
       2. The tablet of  claim 1  wherein the flat sensor and the shielding plate contact each other. 
     
     
       3. The tablet of  claim 1  wherein the flat sensor and the shielding plate are spaced from each other by less than 5 mm. 
     
     
       4. In combination, a tablet, an implement adapted to be moved over an external flat surface of the tablet, the implement including a tuned circuit, the tablet including: a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils arranged in two coordinate directions, the loop coils being disposed between the faces for emitting AC energy coupled to the tuned circuit and responsive to AC energy coupled from the tuned circuit for generating a signal indicative of the implement position relative to the two coordinate directions; and a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on the loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of the AC energy coupled between the loop coils and tuned circuit. 
     
     
       5. The combination of  claim 4  wherein the flat sensor and the shielding plate contact each other. 
     
     
       6. The combination of  claim 4  wherein the flat sensor and the shielding plate are spaced from each other by less than 5 mm. 
     
     
       7. Apparatus for determining the position of an implement adapted to be moved over a surface, the implement including a tuned circuit having a resonant frequency, comprising an AC source of said frequency, a tablet having an exterior surface defining the surface over which the implement is adapted to be moved, the tablet including a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils connected to said AC source, said loop coils being arranged in two coordinate directions and being disposed between the faces for coupling AC energy at said frequency to the tuned circuit and responsive to AC energy coupled from the tuned circuit at said frequency for generating a response indicative of the implement position relative to the two coordinate directions; a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on the loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of the AC energy coupled between the loop coils and tuned circuit, and means responsive to the response for deriving a signal indicative of the implement position. 
     
     
       8. The apparatus of  claim 7  wherein the flat sensor and the shielding plate contact each other. 
     
     
       9. The apparatus of  claim 7  wherein the flat sensor and the shielding plate are spaced from each other by less than 5 mm. 
     
     
       10. A tablet for coupling AC energy to a tuned circuit on an implement adapted to be moved over an external flat surface of the tablet comprising: a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils arranged in two coordinate directions, the loop coils being disposed between the faces for emitting the AC energy coupled to the tuned circuit; and a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of AC energy coupled between the loop coils and tuned circuit. 
     
     
       11. The tablet of  claim 10  wherein the flat sensor and the shielding plate contact each other. 
     
     
       12. The tablet of  claim 10  wherein the flat sensor and the shielding plate are spaced from each other by less than 5 mm. 
     
     
       13. In combination, a tablet, an implement adapted to be moved over an external flat surface of the tablet, the implement including a tuned circuit, the tablet including: a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils arranged in two coordinate directions, the loop coils being disposed between the faces for emitting AC energy coupled to the tuned circuit; and a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on the loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of the AC energy coupled between the loop coils and tuned circuit. 
     
     
       14. The combination of  claim 13  wherein the flat sensor and the shielding plate contact each other. 
     
     
       15. The combination of  claim 13  wherein the flat sensor and the shielding plate are spaced from each other by less than 5 mm. 
     
     
       16. Apparatus for determining the position of an implement adapted to be moved over a surface to be determined, the implement including a tuned circuit having a resonant frequency, comprising an AC source of said frequency, a tablet having an exterior surface defining the surface over which the implement is adapted to be moved, the tablet including a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils connected to said AC source, said loop coils being arranged in two coordinate directions and being disposed between the faces for coupling AC energy at said frequency to the tuned circuit; a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on the loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of the AC energy coupled between the loop coils and tuned circuit, and means responsive to energy coupled between the coils and the tuned circuit for deriving a signal indicative of the implement position. 
     
     
       17. The apparatus of  claim 16  wherein the flat sensor and the shielding plate contact each other. 
     
     
       18. The apparatus of  claim 16  wherein the flat sensor and the shielding plate are spaced from each other by less than 5 mm. 
     
     
       19. A tablet responsive to AC energy from a tuned circuit on an implement adapted to be moved over an external flat surface of the tablet comprising: a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils arranged in two coordinate directions, the loop coils being disposed between the faces and responsive to the AC energy coupled from the tuned circuit for generating a signal indicative of the implement position relative to the two coordinate directions; and a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of AC energy coupled between the loop coils and tuned circuit. 
     
     
       20. The tablet of  claim 19  wherein the flat sensor and the shielding plate contact each other. 
     
     
       21. The tablet of  claim 19  wherein the flat sensor and the shielding plate are spaced from each other by less than 5 mm. 
     
     
       22. In combination, a tablet, an implement adapted to be moved over an external flat surface of the tablet, the implement including a tuned circuit, the tablet including: a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils arranged in two coordinate directions, the loop coils being disposed between the faces and responsive to AC energy coupled from the tuned circuit for generating a signal indicative of the implement position relative to the two coordinate directions; and a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on the loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of the AC energy coupled between the loop coils and tuned circuit. 
     
     
       23. The combination of  claim 22  wherein the flat sensor and the shielding plate contact each other. 
     
     
       24. The combination of  claim 22  wherein the flat sensor and the shielding plate are spaced from each other by less than 5 mm. 
     
     
       25. Apparatus for determining the position of an implement adapted to be moved over a surface, the implement including a tuned circuit having a resonant frequency, comprising an electric AC source including waves of said frequency, a tablet having an exterior surface defining the surface over which the implement is adapted to be moved, the tablet including a flat sensor having a bottom face, a top face defining a predetermined two-dimensional coordinate plane and loop coils connected to said AC source, said loop coils being arranged in two coordinate directions and being disposed between the faces and responsive to AC energy coupled from the tuned circuit at said frequency for generating a response indicative of the implement position relative to the two coordinate directions; a shielding plate disposed under the bottom face of the flat sensor for magnetically shielding the flat sensor, the shielding plate being positioned relative to the flat sensor and being a magnetic material such that it blocks influences on the loop coils caused by external disturbing electromagnetic waves and geomagnetism without causing substantial attenuation of the AC energy coupled between the loop coils and tuned circuit, and means responsive to the response for deriving a signal indicative of the implement position. 
     
     
       26. The apparatus of  claim 25  wherein the flat sensor and the shielding plate contact each other. 
     
     
       27. The apparatus of  claim 25  wherein the flat sensor and the shielding plate are spaced from each other by less than 5 mm. 
     
     
       28. An electromagnetic digitizer, comprising:
   a sensor grid, and        a shield plate disposed under said sensor grid, wherein said shield plate comprises a material with sufficiently high magnetic permeability to increase the magnetic signal in said sensor grid.     
     
     
       29. An electromagnetic digitizer according to  claim 28 , wherein
   said sensor grid includes a sensor grid substrate; and said shield plate is in direct contact with said sensor grid substrate.     
     
     
       30. An electromagnetic digitizer, comprising:
   a sensor grid comprising a multiplicity of wires and a sensor grid substrate,        a pen comprising a pen coil, and        a shield plate disposed under said sensor grid, wherein said shield plate comprises conductive material such that said conductive material is of sufficient thickness and conductivity to prevent penetration of the magnetic field of said pen coil, said shield plate being in contact with said sensor grid substrate.     
     
     
       31. An electromagnetic digitizer according to  claim 30 , wherein
   said shield plate comprises aluminum.     
     
     
       32. An electromagnetic digitizer according to  claim 30 , wherein
   the separation between said shield plate and said wires of said sensor grid is one millimeter or less.     
     
     
       33. An electromagnetic digitizer according to  claim 32 , wherein
   said shield plate comprises aluminum.     
     
     
       34. An electromagnetic digitizer, comprising:
   a shield plate disposed under a sensor grid,        wherein said shield plate comprises a base material of conductive material with a layer of magnetic material disposed on one side of said base material.     
     
     
       35. An electromagnetic digitizer, comprising:
   a shield plate disposed under a sensor grid,        wherein said shield plate comprises a material that increases the magnetic signal in said sensor grid and which prevents penetration of magnetic fields.     
     
     
       36. An electromagnetic digitizer according to  claim 35 , wherein
   said shield material comprises a nickel alloy.     
     
     
       37. An electromagnetic tablet for use in combination with an implement having an electrical impedance element, comprising: a flat sensor for the position of the implement spatially coupled to the electrical impedance element of the implement by AC electromagnetic energy; and a shielding plate arrangement disposed under the flat sensor for magnetically shielding the flat sensor, the shielding plate arrangement being positioned in abutment to the flat sensor and including a magnetic material that blocks influences on the flat sensor caused by external disturbing waves having magnetic components and geomagnetism without causing substantial attenuation of the AC electromagnetic energy so as to obtain a voltage magnitude in the flat sensor sufficient to detect the position of the implement. 
     
     
       38. An electromagnetic tablet according to  claim 29  wherein the flat sensor is electrically coupled to be responsive to an AC source having a frequency of several hundreds of kHz so the sensor is spatially coupled to the impedance element of the implement by AC electromagnetic energy having said frequency. 
     
     
       39. An electromagnetic tablet according to  claim 29  wherein the magnetic material includes silicon steel containing  4 . 0  to  7 . 0  weight percent of silicon. 
     
     
       40. An electromagnetic tablet according to  claim 29  wherein the shielding plate arrangement includes a magnetic shield plate and a non- magnetic metal plate, the magnetic shield plate being disposed between the flat sensor and the non - magnetic metal plate.